so… You made a custom object File__c and you attach files to it and then reference it from multiple objects?
If I am understanding you correctly, I think the best/fastest solutions would to be to do one or the other:
A) make several of these file__c objects and make each a child of the parent that will be referencing it. You und up with multiple repositories, but each one will follow the permissions of its parent.
Or have a junction object. I haven’t fully thought this through, but if you create a junction object, it seems that you could create a snazzy way to create a FileJunction__c record that is a child of the parent object and then create the File__c record as a lookup of FileJunction__c. I think this gets you a quasi many-to-many relationship with inherited sharing that you are looking for, but I haven’t thought very much about it, so if it doesn’t work don’t Skuidshame me! If it does work, then you only eat up one master-child relationship on each object which would be to that objects FileJunction__c object. You would still have a single repository for files in File__c. Each object would need its own junction, though, for you to get inherited sharing.

I edited my response above. I meant A or B not A and B.

Sorry. My mistake. skuid__Image__c is the object that I should be referencing.

In either case, the junction object may work. Instead of linking skuid__image__c to a contact, you could link it to Contact_File_Junction__c and make Contact_File_Junction__c a child of Contacts. Then you would have a “gate” between the the contact and the file that would inherit the permissions of the Contact.

That’s my issue. I want to continue using the Skuid field renderer for File Upload as is.

I guess what I am thinking is that now you are using that field on the Contact object. Instead, have the contact object open a pop up that creates a new junction record child of that contact. Then have the junction record have the Skuid field for file upload. A bit convoluted, but it may be the easiest way for you to get your sharing model worked out.